The purpose is to investigate the normal and abnormal development of binocularity in humans using the visually evoked potential (VEP) as a response measure. Three separate, operationally distinct binocular phenomena will be examined; binocular suppression, binocular summation, and stereopsis. Eight major groups of subjects will be tested; normal adults, normal school children, normal preschool children, normal infants, abnormal adults, abnormal school children, abnormal preschool children, and abnormal adults. For any given experiment stimulus, parameters and the response system (VEPs) will be held constant, permitting quantification of the changes in development or the difference between normals and abnormals. A behavioral measure of visual preference, percentage of time looking at the stimulus, determined as the VEPs are collected will enable one to relate the VEPs to behavior in infants. Across experiments, the basic stimulus conditions will remain constant. Gratings will be the stimuli, and the eyes will be dissociated using the anaglyphic method. This similarity of stimulus variables should make comparisons of differences between binocular processes, e.g., different maturation rates, easier to assess. During the third and fourth years of the project, the knowledge gained in earlier project years will be employed in the construction and validation of clinical measures of binocularity in infants and preverbal children. Measures of binocularity should be of value in the assessment of developmental disorders of binocularity strabismus, anisometropia, and amplyopia and the assessment of the effectiveness of treatments of these disorders.